An optical scanner using a Micro-Electro-Mechanical Systems (MEMS) mirror has been used in a laser printer, a projection type display apparatus and the like. FIG. 9 shows a related-art optical scanner 100. The related-art optical scanner includes a base plate 110, a driving portion 111 that is formed on the base plate 110, a pair of torsion beam portions 112 that are connected to the base plate 110 and a mirror portion 113 that is supported by the pair of torsion beam portions 112 and has a reflective surface configured to reflect incident light. The driving portion 111 has a piezoelectric element. When a voltage is applied to the driving portion 111, the piezoelectric element of the driving portion 111 causes bending deformation in a portion of the base plate 110 in proximity to the driving portion 111. The bending deformation caused in the base plate 110 generates a plate wave on the base plate 110. The plate wave generated on the base plate 110 produces a rotational moment in the mirror portion 113 supported by the torsion beam portions 112 and the torsion beam portions 112. The rotational moment causes the mirror portion 113 and the torsion beam portions 112 to be torsionally vibrated. As the mirror portion 113 and the torsion beam portions 112 are torsionally vibrated, the mirror portion 113 is oscillated. As the mirror portion 113 is oscillated, the light incident on the reflective surface of the mirror portion 113 is scanned.
However, in order to achieve a large optical deflection angle, it is required to torsionally vibrate the mirror portion 113 largely. When the mirror portion 113 is largely oscillated, dynamic distortion of the mirror portion 113 becomes large. As a result, it becomes difficult to perform a high precision scanning.